As senior officials invited Polish vets to examine the meat and relevant documentation, Simon Coveney confirmed Garda officers were heavily involved in a major investigation.

Northern Ireland's Deputy First Minister Martin McGuinness has also called for a Police Service of Northern Ireland (PSNI) inquiry as the affair threatens confidence in Ireland's meat industry and the future of a number of companies on both sides of the border.

Mr Coveney told deputies and senators in the Irish Parliament he did not want to prejudice an investigation, but promised: "Very significant resources have been deployed by my department and the Food Safety Authority of Ireland initially to find the source of this food incident so that consumers can be fully reassured and now also to consider whether there is fraudulent or criminal activity involved."

"This is a matter of reputation, obviously we cannot afford to have that," Mr Kenny said.

Rangeland Foods in Co Monaghan was one of the latest plants shut down after a sample at the factory tested positive with a reading of 75% horse DNA in raw ingredients, authorities said.

It supplies burgers to one of Ireland's most popular fast food chains, Supermac's, but the restaurant's chief executive Pat McDonagh has insisted he is sure all his burgers are 100% Irish.

The highest level of equine genetic material has been found in a quantity of frozen meat being stored in Northern Ireland.

Freeza Meats in Newry had meat which was 80% horse, which the UK's Food Standards Agency (FSA) said was potentially linked to the Silvercrest factory in the Republic of Ireland, one of the first processors to be named in the scandal. The meat has not entered the food chain and was not purchased by Freeza, a spokesman for the company said.